This invention relates to medical diagnostic devices, and in particular, to devices for measurement of pressure within the heart.
The pressure within the left ventricle of the heart is an important parameter in the treatment of heart disease. However, the measurement of that pressure is hampered by the need to insert a probe into the left ventricle. Such invasive measurements are costly, time-consuming, and potentially dangerous to the patient. As a result, despite its importance, the pressure within the left ventricle is only rarely measured directly.
There exist systems for non-invasively measuring left-ventricular pressure during limited portions of the cardiac cycle. For example, during the ejection phase, and in the absence of aortic valve disease, the left-ventricular pressure corresponds to the arterial pressure. During that portion of the cardiac cycle characterized by an open mitral valve, the left-ventricular pressure is (to the extent that the mitral valve is normal) virtually the same as the left-atrial pressure. This left-atrial pressure is in turn related to PCWP (pulmonary capillary wedge pressure), which can be measured non-invasively by using a device and methods described in McIntyre, U.S. Pat. No. 5,291,895, the contents of which are herein incorporated by reference.
The invention provides software for extracting segments from the outputs of two or more non-invasive diagnostic devices, each of which provides data that is indicative of left-ventricular pressure over at least a portion of the cardiac cycle. As used herein, data indicative of left-ventricular pressure includes absolute and relative pressure data, as well as data showing a contour of a pressure waveform. The software of the invention then time-shifts the extracted segments to inscribe a continuous curve indicative of the left-ventricular pressure waveform.
In one practice of the invention, a left-ventricular pressure waveform is assembled by obtaining a first pressure waveform from a first non-invasive pressure measurement and a second pressure waveform from a second non-invasive pressure measurement. First and second segments are then selected from the first and second waveforms respectively. These segments are associated with first and second intervals of the cardiac cycle. The first and second segments are then time-shifted relative to each other by an amount indicative of a relative time of occurrence of each of the first and second segments.
As used herein, xe2x80x9cpressure measurementxe2x80x9d refers to the collection of data indicative of pressure, which, as defined earlier, means absolute and relative pressure data, as well as data showing or recording a contour of a pressure waveform.
The first pressure waveform can be a signal indicative of a left-atrial pressure or one indicative of arterial pressure. When the signal indicates left-atrial pressure, the method can include obtaining a shape of the waveform from an apex cardiogram and adjusting an amplitude of the waveform on the basis of a non-invasively measured diastolic pressure.
Selecting a first segment can include determining an occurrence of an event indicative of the first interval of the cardiac cycle. A suitable choice of event is activity of a heart valve, for example the mitral valve or the aortic valve. An easily detectable event is, for example, the transition of either the mitral valve or the aortic valve between an open state and a closed state. Such events can be identified by detecting an acoustic signature indicative of valve activity, by detecting an electrical signature indicative of valve activity, or by detecting a mechanical signature indicative of valve activity.